“Wi REPORT—1857. 
the case is one which brings us still nearer to the question at issue, inasmuch 
as the laws which have been obtained—and they are numerous—have resulted 
from a method of inquiry altogether similar to that adopted in Meteorology. 
Time will not permit me to inquire whether there is not a misconception 
of a metaphysical kind at the root of this objection. I may observe, how- 
ever, before leaving the subject, that there are two modes of studying the 
sequences of natural phenomena,—one in their relation ¢o time, and which is 
best accomplished by observations at stated periods, and the other in the 
relation of the successive phases of the phenomenon to ane another. Of these, 
the latter, although not wholly neglected, has not been so much followed as 
it deserves; and I cannot but think that it would, if more systematically 
followed, enrich the science of Meteorology with a new harvest of results. 
The most important of the recent additions to the theory of Light have 
been those made by M. Jamin. It has been long known that metals differed 
from transparent bodies, in their action on light, in this, that plane-polarized 
light reflected from their surfaces became elliptically polarized; and the 
phenomenon is explained, on the principles of the wave-theory, by the 
assumption that the vibration of the ether undergoes a change of phase at 
the instant of reflexion, the amount of which is dependent on its direction, 
and on the angle of incidence. This supposed distinction, however, was 
soon found not to be absolute. Mr. Airy showed that diamond reflected 
light in a manner similar to metals; and Mr. Dale and Professor Powell ex- 
tended the property to all bodies having a high refractive power. But it 
was not until lately that M. Jamin proved that there is xo distinction, in this 
respect, between transparent and metallic bodies ; and that all bodies trans- 
form plane-polarized into elliptically-polarized light, and impress a change 
of phase at the moment of reflexion. Professor Haughton has followed up 
the researches of M. Jamin, and established the existence of cireularly- 
polarized light by reflexion from transparent surfaces. 
The theoretical investigations connected with this subject afford a re- 
markable illustration of one of those impediments to the progress of Natural 
Philosophy, which Bacon has put in the foremost place among his examples 
of the Idola,—I mean the tendency of the human mind to suppose a greater 
simplicity and uniformity in nature than exists there. The phenomena of 
polarization compel us to admit that the sensible luminous vibrations are 
transversal, or in the plane of the wave itself ; and it was naturally supposed 
by Fresnel, and after him by MacCullagh and Neumann, either that no 
normal vibrations were propagated, or that, if-they were, they were uncon- 
nected with the phenomena of light. We now learn that it is by them that 
the phase is modified in the act of reflexion; and that, consequently, no 
dynamical theory which neglects them, or sets them aside, can be complete. 
Attention has been lately recalled to a fundamental position of the wave- 
theory of light, respecting which opposite assumptions have been made. 
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